Boulder – Prosecutors have added a first-degree murder charge against a 15-year-old girl whose mother was stabbed to death and then left in the trunk of a car for three weeks.

Tess Damm was originally charged with conspiracy to commit first-degree murder after the body of her mother, 52-year-old Linda Damm, was found on Feb. 28. The body was in the back of Linda Damm’s car in the garage of her home in Lafayette, about 20 miles north of Denver.

The first-degree murder charge was filed last week and made public Monday. It was not immediately clear why the additional charge was filed, and neither prosecutors nor Damm’s attorney, Beth Kelley, returned calls.

Tess Damm is being prosecuted as an adult. Conviction on a first-degree murder charge carries a sentence of up to life in prison. The sentence for conspiracy to commit first-degree murder is 16 to 48 years in prison.

She also faces charges of being an accessory to a crime and tampering with physical evidence.

Her boyfriend, Bryan Grove, 17, faces charges of first-degree murder, conspiracy to commit first-degree murder and tampering with physical evidence. He also is being prosecuted as an adult.

Jared Smith, 16, accused of helping put Linda Damm’s body in the car, has pleaded guilty to being an accessory and was sentenced to two years in youth corrections and six months of parole.

Jared Guy, 18, accused of helping in attempts to dispose of the body, has pleaded not guilty to accessory and evidence-tampering charges. His trial is set for Sept. 10.

Police have said they believe Grove stabbed Linda Damm to death during an argument on Feb. 4. Police said Tess Damm, Grove and Guy tried twice to get rid of the body but failed, once because their vehicle got stuck and once because they feared they would be discovered.

Investigators said the teens were planning a third attempt to dump the body when they were arrested.

They said Tess Damm had been living in her mother’s house along with Grove for weeks after the stabbing.

The University of Colorado leadership is grappling with how to address a nationwide nosedive in the favorability of higher education — particularly, among conservatives — as CU’s own representatives and decision-makers disagree on what’s behind the downturn.